The first book of the work "On the Section of a Line" is preserved in Arabic. The work deals with the solution of a single problem, which is as follows: "From a given point, bring a straight line that intersects, from two given lines in position and up to certain given points that lie on them, segments that have a ratio equal to a given ratio." The problem admits a large number of solutions. In the first book, the first 24 cases of the problem are solved.